Waveguide for moisture measurement

ABSTRACT

Waveguide for use in moisture measurement comprises two plates with the propagation channel partly formed in each. Preferably both plates have a series of spaced grooves or slots at preferably both sides of the channel and transverse thereto to reduce longitudinal excitation of electromagnetic waves outside the channel.

United States Patent 1 [111 3,720,890 Anderson I 1March 13, 1973 1 1 WAVEGUIDE FOR MOISTURE FOREIGN PATENTS 0R APPLICATIONS MEASUREMENT 844,856 8/1960 Great Britain ..333/98 R [75] Inventor: John Gordon Anderson, Northumberland England OTHER PUBLICATIONS [73] A i Th R k O i i Li i Summerhill, S.; Microwaves In The Measurement of London, En land Moisture lnstrument Review; Oct. 1967; pp 419-422 [22] Filed: July 8,1971

App1.No.: 160,928

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,586,971 6/1971 Bosisic ..324/58.5 C

Primary Examiner-Robert J. Corcoran Attorney-Holcombc, Wetherill & Brisebois [57] ABSTRACT Waveguide for use in moisture measurement comprises two plates with the propagation channel partly formed in each'. Preferably both plates have a series of spaced grooves or slots at preferably both sides of the channel and transverse thereto to reduce longitudinal excitation of electromagnetic waves outside the channel.

7 Claims, 3 Drawing Figures PATENTEDHAR13 1915 SHEET 10? 2 PATENTED MAR 1 3 I975 SHEET 2 OF 2 WAVEGUIDE FOR MOISTURE MEASUREMENT This invention relates to waveguides, particularly but not exclusively waveguides for use in measuring the moisture content in sheet materials.

lt is well known that any moisture in a sheet material lying between the halves of a split waveguide will altenuate the micro waves propagated along the waveguide propagation channel. The energies of the micro waves before and after contact with the sheet material give the attenuation and hence an indication of the moisture content in the sheet material. The sheet material may be stationary or moving, the guide being appropriately designed in the latter case.

A disadvantage of such a waveguide however is that unless the sheet material fills the gap between the guide plates exactly, then there is always the possibility that electromagnetic energy will radiate from the propagation channel allowing the electric field to excite longitudinally in the gap between the plates and outside the propagation channel, thus causing electromagnetic energy to propagate in the area surrounding the propagation channel. Such propagation energy may be lost by radiation or may couple into another part of the waveguide causing errors in moisture determination.

It is an object of this invention to provide a waveguide wherein the aforesaid disadvantage is obviated or mitigated.

According to the invention there is provided a waveguide comprising two plates arranged in face to face relationship with the propagation channel partly formed in each of the opposed faces of the plates and wherein at least one of said opposed faces has slots or grooves which are spaced in the direction of the length of the propagation channel, which are located at at least one side of the propagation channel, and each of which extends in a direction transverse to the direction of the length of the propagation channel but does not penetrate such channel so that said slots can act to reduce or eliminate longitudinal excitation of electromagnetic waves outside the propagation channel.

Preferably, there is a series of such slots or grooves at each side of the propagation channel.

Preferably, each of said slots or grooves has a curved base which leads to the surface of the waveguide plate, one end of such base terminating close to the propagation channel.

Preferably also, each waveguide plate has such slots or grooves.

There may be, in one or both of the waveguide plates, one or more choke channels extending transversely of and through the transverse grooves or slots.

There may be a dielectric material holding channel extending transversely of, and passing through, the grooves or slots.

Preferably, there is a lossy dielectric material in the or each dielectric holding channel, the transverse slots or grooves passing through such material.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional elevation taken through one plate ofa split waveguide;

FIG. 2 is a diagrammatic sectional elevation taken through the ,part of waveguide when the plates are operatively positioned in relation to the sheet material to be tested; and

FIG. 3 is a perspective view of part of one of the waveguide plates, and shows the plate face in which the propagation channel is partly formed.

Referring to the drawings, firstly to FIG. 1, waveguide plate shown therein is represented by the reference numeral 10 and a part of the propagation channel formed in such plate 10 by the reference numeral 12, such channel 12 extending in a direction normal to the plane containing FIG. 1. In the completed waveguide the three channel sections 12 are joined end to end to form a continuous propagation channel.

lnterspaced with the propagation channels 12 and extending parallel thereto are dielectric material holding channels 14 each containing the rectangular section rod of dielectric material 4. The channels 14 are formed on the same side of the plate 10 as the channel sections 12.

Interspaced between the channel sections 12 and channels 14 are choke channels .3 which are parallel both to the channel sections 12 and the channels 14 and are also formed in the same face of the plate as sections 12 and channels 14.

Extending transversely from each side of each channel section 12 is a series of spaced slots 5 which extend through the dielectric material 4 as shown in FIG. 3 and each of which is defined by grill walls and has a curved base of the form shown in the drawings so that the depth of the slot decreases to zero at'each end and the along the edges of the channel sections 12 are external to the electromagnetic path of the waveguide and interupt the longitudinal conducting, surface immediately external to the aforesaid channel.

Referring now to FIG. 2, the other plate 16 of the waveguide has been shown as not having any choke channels 3 but it is to be appreciated that this omission is optional and if desired the plate: 16 may be provided with such channels 3 and therefore, be identical to plate 10. It is also to be noted that in FIG. 3 only two choke channels 3 have been shown. This is simply in the interest of clarity of the drawing. p

In using the waveguide in the manner indicated in FIG. 2 with a material to be tested positioned between the plates as indicated at l in FIG. 2, longitudinal propagation of energy along the propagation channel direction but external to the channel is prevented by the slots 5 which are so spaced as not to have a dimensional or periodic spacing which is an integral fraction of the wavelength of the electromagnetic radiation in order to prevent resonances :in the longitudinal direction. Energy escaping past the high electrical impedance created by the resonance slot or choke 3 is absorbed by the lossy material bars 4 and therefore, using this waveguide it is to be expected that the results obtained in measuring the moisture content of sheet material such as sheet 1 would be more accurate than using a waveguide without the slots 5.

lclaim:

l. A waveguide comprising two plates arranged in face to face relationship with the propagation channel partly formed in each of the opposed faces of the plates and wherein at least one of said opposed faces has slots or grooves which are spaced in the direction of the length of the propagation channel, which are located at at least one side of the propagation channel, and each of which extends in a direction transverse to the direction of the length of the propagation channel but does not penetrate such channel so that said slots act to reduce or eliminate longitudinal excitation of electromagnetic waves outside the propagation channel.

2. A waveguide according to claim 1, wherein there is a series of such slots or grooves at each side of the propagation channel.

3. A waveguide according to claim 2, wherein each of said slots or grooves is defined by side walls and a curved base and diminishes to zero depth at each end,

one end of such base terminating close to the propagation channel.

4. A waveguide according to claim 3, wherein each waveguide plate has such slots or grooves.

5. A waveguide according to claim 4, wherein there is at least one choke channel in at least one of the waveguide plates extending transversely of and through the transverse grooves or slots.

6. A waveguide according to claim 1, wherein there is a dielectric material holding channel extending transversely of, and passing through, the grooves or slots.

7. A waveguide according to claim 6, wherein there is a lossy dielectric material in each dielectric holding channel, the transverse slots or grooves passing through such material. 

1. A waveguide comprising two plates arranged in face to face relationship with the propagation channel partly formed in each of the opposed faces of the plates and wherein at least one of said opposed faces has slots or grooves which are spaced in the direction of the length of the propagation channel, which are located at at least one side of the propagation channel, and each of which extends in a direction transverse to the direction of the length of the propagation channel but does not penetrate such channel so that said slots act to reduce or eliminate longitudinal excitation of electromagnetic waves outside the prOpagation channel.
 1. A waveguide comprising two plates arranged in face to face relationship with the propagation channel partly formed in each of the opposed faces of the plates and wherein at least one of said opposed faces has slots or grooves which are spaced in the direction of the length of the propagation channel, which are located at at least one side of the propagation channel, and each of which extends in a direction transverse to the direction of the length of the propagation channel but does not penetrate such channel so that said slots act to reduce or eliminate longitudinal excitation of electromagnetic waves outside the prOpagation channel.
 2. A waveguide according to claim 1, wherein there is a series of such slots or grooves at each side of the propagation channel.
 3. A waveguide according to claim 2, wherein each of said slots or grooves is defined by side walls and a curved base and diminishes to zero depth at each end, one end of such base terminating close to the propagation channel.
 4. A waveguide according to claim 3, wherein each waveguide plate has such slots or grooves.
 5. A waveguide according to claim 4, wherein there is at least one choke channel in at least one of the waveguide plates extending transversely of and through the transverse grooves or slots.
 6. A waveguide according to claim 1, wherein there is a dielectric material holding channel extending transversely of, and passing through, the grooves or slots. 